Story run about noble's unreasonable request (4,5)
I believe the answer is:
tall order
'unreasonable request' is the definition.
(I've seen this before)
'story run about noble's' is the wordplay.
'story run' becomes 'taler' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'about' indicates putting letters inside.
'noble' becomes 'lord' (synonyms).
'taler' placed around 'lord' is 'TALL ORDER'.
Can you help me to learn more?
(Other definitions for tall order that I've seen before include "hard to fulfil?" , "as the building of Babel was?" , "Challenge" , "I want a skyscraper built by tomorrow" , "delivery of sequoias?" .)